This invention relates to an apparatus and method for collecting emitted light, preferably in the x-ray emission spectrum. More particularly, this invention provides a collimator and focusing optic that can collect and direct emitted light, such as in short wavelength radiation lithography and non-lithography operations.
In a generally known, x-ray lithography process, the baseline x-ray source is a synchrotron. The synchrotron ultimately produces a collimated x-ray beam from x-rays generated from an accelerated electron beam. When integrated with an advanced x-ray stepper, which includes a mask, resist and wafer such an apparatus, has produced sub-tenth micron transistor gates. Since the synchrotron can produce high power, and high wafer throughput has been possible.
However, there are several disadvantages associated with the use of such a synchrotron based apparatus. For example, known synchotrons are very large, taking up a relatively large amount of space. They also are expensive. Generally the use of a number of steppers is necessary to make them cost effective. There has been some reluctance by industry to adopt a synchotron-based x-ray lithography process because of the high cost and time required to modify current factory designs to accommodate synchrotrons.
In nonlithography applications, such as x-ray tomography, synchrotrons also have been used as the x-ray radiation source. As in x-ray lithography, the synchrotron suffers the disadvantages of high cost and inconvenience. A point x-ray source could be used, but a large collection angle collimator/focusing optic is needed.
For these reasons and others, there is a need for an x-ray source that can be cost effectively used with a single stepper and is similar in size to the current advanced optical stepper light sources, such as a deep ultraviolet excimer laser. Several attempts have been made to develop such a x-ray source including laser plasma, dense plasma focus, and electron beam systems. Although significant x-ray power can be generated from these x-ray point sources, they suffer a disadvantage in that the radiation is emitted into angles of 2xcfx80 to 4xcfx80 steradians.
Various apparatus have been used to attempt to redirect a point source radiation emission field using x-ray optics to redirect x-rays emitted into a uniform intensity and collimated beam. One example is a polycapillary glass tubes and another is a microchannel plate. Solid angles of 0.048 steradian of 1.1 nanometers laser-plasma radiation have been collimated with polycapillary tubes and produced uniform intensities. However, these apparatus have collimated only a relatively small solid angle of the emitted x-ray field. There is a need for an apparatus that can collimate a greater portion of the x-rays emitted from such a point source and thereby more efficiently collect and collimate the available point-source radiation.
The solid angle that can be collected and collimated also can be enhanced by using a grazing incidence x-ray reflector or a variable thickness x-ray resonance coating reflector. Resonance coatings have been developed to increase the x-ray critical reflection angle and for 1.1 nanometer radiation, solid angles of 0.21 steradians can be collimated. This solid angle is approximately four times greater than the polycapillary collimator alone. Collimation is achieved with a conical or parabolic reflector with a variable thickness multi-layer x-ray reflective coating.
However, this apparatus suffers a disadvantage in that it does not achieve a highly collimated x-ray beam in the region of the axis of the collimator. To achieve a highly collimated beam, a beam block typically is used in the central portion of the collimator and consequently a toroidal x-ray beam is produced. A further disadvantage of this apparatus is that during operation, the collimator must be scanned across the wafer to achieve uniform x-ray exposure on the wafer. Scanning is an added complication and reduces the efficiency of the process and increases the cost of the system.
Accordingly, there is a need for an x-ray collimator that achieves a relatively high solid angle collimation and uniform intensity across the entire output aperture.
The present invention alleviates to a great extent the disadvantages of the known apparatus and methods for collimating short wavelength light, such as radiation in the x-ray spectrum or light with wavelengths less than about 13 nanometers or other wavelengths that can be suitably reflected and collimated in accordance with the present invention. In particular, the present invention provides a high gain x-ray collimator producing a generally uniform intensity profile. In the present invention, a hybrid reflector (such as a grazing incidence reflector or resonance reflective optic) and guide channel (such as using polycapillary tubes or microchannel plates) is provided. This is of particular utility in x-ray lithography. A focusing optic is also provided for use in non-lithography applications, such as tomography, x-ray photoelectron spectroscopy, x-ray diffraction, x-ray microscopy and x-ray flourescence.
The guide channel can be made of polycapillary tubes, microchannel plates or a combination of polycapillary tubes and microchannel plates. The guide channel collimates or focuses the central portion of the x-ray beam in a desired shape, such as circular, elliptic, square, or rectangular shape. The reflector can be made of any suitable reflective optic that can reflect the particular light (such as x-rays or ultraviolet) in the desired fashion. For example, parabolic resonance reflector with a shape similar to the polycapillary collimator is used to increase the solid angle collected and produce a circular, square, etc. annular x-ray beam whose inside dimensions are approximately equal to the exit dimensions of the polycapillary collimator. The annular beam shape, intensity profile and collimation angle is adjusted, if necessary, by an absorber, or polycapillary tubes to provide the desired intensity profile at the exit aperture of the hybrid x-ray collimator optic.
The reflector may optionally be a focusing optic in order to focus the collimated light to a desired spot. For example, an elliptical profile can be used as a focusing optic; alternatively, a focusing optic is obtained by placing two generally parabolic reflector optics arranged end-to-end, although the reflector optics need not be identical.
It is an advantage of the present invention is that the solid angle of the collected radiation is increased. Another advantage of the present invention is that the amount of collimated power delivered by the collimator is increased due to increasing the solid angle in which radiation is collected. A further advantage of the present invention is that the throughput of exposed wavers in an x-ray lithography process can be increased in that that there is a greater collimated power delivery and that the need for scanning the collimator is reduced because of the greater power delivery.